1. Field of the Invention
Embodiments of the present invention generally relate to voltage detection techniques and, more particularly, to a method and apparatus for detecting a zero-voltage condition across four-quadrant switches.
2. Description of the Related Art
There are circuit topologies for power conversion which use zero voltage switching (ZVS) as a technique for reducing switching losses and thus improving efficiency. There are topologies emerging which use four-quadrant (4Q) switches operating with ZVS. 4Q switches conduct either polarity of current and block either polarity of voltage, and are commonly composed of two MOSFET switches connected in series with a common-source configuration. The ZVS transitions can be quite fast (e.g., tens of nanoseconds (ns)) and efficiency can be lost if a switch is not turned on at the appropriate time. Thus the circuit needs to detect when the voltage across a switch is relatively close to zero volts in a very fast manner.
Zero-voltage detectors in use today are limited to functioning over fixed and low voltage ranges and are not able to trigger at certain voltage levels. Often, these zero-voltage detectors only function with one polarity of voltage. A simple way of detecting zero-voltage transition used in the market involves a voltage comparator device. For example, a 4Q switch made of two switches in series connected to a common point (a local ground) may be connected to voltage dividers going to a voltage comparator in order to detect a zero-voltage condition across the 4Q switch. The resistors in the voltage dividers must have high resistances, otherwise a large amount of current will flow through causing power dissipation. However, the high resistance values coupled with intrinsic capacitance of the device itself create a low-pass filter, reducing the detection speed of the zero-voltage detector significantly. Thus the detector's usefulness is decreased in applications where voltage transitions occur very rapidly. In addition, zero-voltage detectors which are able to detect fast switching are often component heavy and consume excessive power.
Therefore, there is a need in the art for a faster and more efficient method and apparatus for detecting zero-voltage conditions across four quadrant switches.